Antisense oligonucleotides with improved binding affinity for RNA targets and improved in vivo nuclease resistance will be developed using carbohydrate modifications at the 2'-position (RNA mimetics). The novel modification 2'-DMAOE (2'-O-(dimethylaminooxyethyl) will be evaluated as (i) a Gapmer antisense oligonucleotide which will work by an RNase H dependent mechanism, and (ii) a uniform (P=O) antisense oligonucleotide which will work by inhibition of the function of m-RNA target by a non- RNase H mechanism (translation arrest). Synthesis of required 2'- DMAOE RNA phosphoramidites will be based on 2'-alkylation chemistry developed at Isis. The gapmer antisense oligonucleotide targeted against H-ras mRNA will be evaluated for improved affinity, nuclease resistance and hence improved RNase H activity in biophysical and in vitro assays. Scrambled control oligonucleotides will be used to demonstrate antisense activity. Improved nuclease resistance will be tested in in vivo mouse plasma, kidney and liver. In HCV target, oligonucleotide will be used as P=O uniform modification and hence will be evaluated for its activity based on translation arrest mechanism for the inhibition of HCV protein expression. PROPOSED COMMERCIAL APPLICATIONS: Therapeutic antisense oligonucleotides are potentially a multibillion-dollar industry. Commercialization of antisense oligonucleotides against viral, cellular and cancer targets is limited by the pharmacokinetic and pharmcodynamic properties of existing first generation 2'-deoxy phosphorothioate drugs. RNA modifications which enhance target affinity and biostability can lead to antisense drugs of (i) shorter length (which translates to improved absorption and lower production cost), and (ii) less frequent dosing, and (iii) higher target specificity, and hence less toxicity.